1. Field of the Invention
The present invention relates to lost circulation additives, to lost circulation treatment fluids made therefrom, to methods of minimizing lost circulation in a well. In another aspect, the present invention relates to lost circulation additives comprising polymer and fibers or comminuted plant materials, to lost circulation treatment fluids made therefrom, to methods of minimizing lost circulation in a well using such fluids.
2. Description of the Related Art
Subterranean wells are utilized to reach desirable oil and/or gas bearing formations, and are generally drilled utilizing rotary drilling techniques. In such rotary drilling of wells for oil and gas, drilling fluids ("muds") are circulated into the well through hollow tubular drill pipe, past the teeth of the cutter head to sweep away the cuttings from the cutter head, and returned to the surface along with the cuttings through the annulus surrounding the drill pipe. The drilling fluid is generally circulated in such a manner as to remove drill cuttings to prevent clogging of the cutter and to support the walls of the well hole. Such drill cuttings are entrained in the drilling fluid and brought to the surface with the fluid and then screened out and discarded. In addition to removing drill cuttings and supporting the walls of the well hole, the drilling fluid also serves to cool and lubricate the drill bit and, in the case of systems employing downhole drill motors, it functions as a power fluid for the drill motor.
Typically, drilling fluids may be water-base, employing a base of fresh water, salt water, or an oil-in-water emulsion in which water forms the continuous phase, or oil-base, employing a relatively pure oil such as crude petroleum oil or diesel oil, or in may be an "invert" emulsion, a water-in-oil emulsion in which oil forms the continuous phase or a synthetic base employing a polymer.
Drilling fluids normally contain clays and/or other dispersed solids which are employed to impart desired rheological properties to the drilling fluid. Not only do these clays and/or other suspended solids impart desirable thixotropic properties to the drilling fluid, they also serve to coat the walls of the well with a relatively impermeable sheath, commonly termed a filter cake, which retards the flow of fluid from the well into the surrounding subterranean formations.
In addition to clays and/or other suspended particles, a drilling fluid may also contain one or more weighting agents which function to increase the density of the fluid to a level which will offset high pressures encountered during the drilling operation. Non-limiting examples of suitable weighting agents which may be used in either water base or oil base drilling fluids include heavy minerals such as barite and gelena.
One problem very commonly encountered during rotary drilling operations is the problem of lost circulation in which part or all of the drilling fluid is not returned to the surface. This problem may manifest itself anywhere from moderate losses of the drilling fluid, to substantial or even total losses of the drilling fluid such that little or none of it is returned to the surface. Where a formation zone is identified in which unacceptably large amounts of drilling fluid is lost, such formation zone is commonly termed a "loss zone" or a loss circulation zone." While there are many causes for loss circulation, non-limiting examples include those situations when the well encounters a formation of unusually high permeability or one which has naturally occurring horizontal or vertical fractures or fissures. Also, the formation may be fractured accidentally by the hydrostatic pressure exerted by the drilling mud, particularly when a change over to a relatively heavy mud is made in order to control high formation pressures.
As can be expected, over the years numerous techniques have been developed to prevent or reduce loss circulation. One common technique where the loss circulation is not so severe is to add various fluid loss agents which function to change the rheological properties of the drilling mud in order to increase its resistence to flow from the well bore into the formation. Such fluid loss agents include synthetic polymeric thickening agents such as partially hydrolyzed polyacrylamide, polyelectrolite such as an ionic polysaccharide, various gums such as locust bean gum and guar gum, various starches, and carboxymethylcellulose (CMC) or carboxyethylcellulose (CEC).
Where the loss circulation is more severe, it is a normal practice to incorporate into the drilling mud various bulk materials which function to combat or prevent loss circulation. It has been common in the past to add any number of materials to the drilling fluid which act to reduce or prevent flow of the drilling fluid from the well hole to the formation. These materials are commonly referred to as "loss (or lost) circulation additives". Such prior art loss circulation materials include fibrous, flake (or laminated), and granular materials. A nonexhaustive list of such loss circulation includes nut and seed shells or hulls (peanut almond, walnut, peach, brazil, coconut, peanut, sunflower, flax, cocoa bean, cottonseed, rice, linseed); crude pectate pulp; feathers; citrus pulp; beet pulp; peat moss fibers; jute; flax; mohair; lechuguilla fibers; cotton; cotton linters; wool; paper; wet-strength paper; sugar cane; bagasse; bamboo; corn stalks; sawdust; straw; wood fiber; cedar fiber; bark chips; cork; popped popcorn; dehydrated vegetable matter (suitably dehydrated carbohydrates such as citrus pulp, oatmeal, tapioca, rice grains, potatoes, carrots, beets, and various grain sorghams); the ground woody ring portion of corn cobs; whole ground corn cobs; hydrophobic, organophilic, water-wettable fibrous materials such as treated cotton, dried bagasse, and dried peat fibers; and specific mixtures of these materials. Many assorted inorganic materials have also been utilized as loss circulation materials.
Seepage losses can occur to any type of loss zone and in any type of formation when the particles in the drilling fluid are not fine enough to complete the seal. It has been established that the maximum allowable drilling fluid loss is on the order of 1 bbl/hr (0.16m.sup.3 /h), as measured in the mud pit at the surface.
There are numerous examples of patents teaching the use of various types of materials for use as lost circulation additives in drill fluids. The following are not an exhaustive sampling.
U.S. Pat. No. 2,610,149, issued Sep. 9, 1952, to Van Dyke, discloses the use of corn stalks, wood shavings, flake cellophane and chopped up paper in drilling fluids.
U.S. Pat. No. 2,779,417, issued Jan. 29, 1957, to Clark et al., discloses the use of cellophane, rice hulls and shredded paper as bridging agents in a well fluid.
U.S. Pat. No. 4,247,403, issued Jan. 27, 1981, to Foley et al., discloses the use of whole corncobs or the woody ring portion of corncobs as loss circulation additives for drilling fluids.
U.S. Pat. No. 4,474,665, issued Oct. 2, 1984 to Green, discloses a lost circulation material useful in drilling fluids formed from cocoa bean shell material having a particle size distribution from 2 to 100 mesh.
U.S. Pat. No. 4,579,668, issued Apr. 1, 1986 to Messenger, discloses for use as drilling fluid bridging agents, ground walnut shells, cellophane and shredded wood.
U.S. Pat. No. 5,004,553, issued Apr. 2, 1991, and U.S. Pat. No. 5,071,575, issued Dec. 10, 1991, both to House et al., disclose a well working composition containing oat hulls and optionally including one or more of ground corn cobs, cotton, citrus pulp, and ground cotton burrs.
U.S. Pat. No. 5,076,944, issued Dec. 31, 1991 to Cowan et al., discloses a seepage loss additive comprising ground cotton burrs in combination with one or more of ground oat hulls, ground corn cobs, cotton, ground citrus pulp, ground peanut shells, ground rice hulls, and ground nut shells.
U.S. Pat. No. 5,118,664, issued Jun. 2, 1992, and U.S. Pat. No. 5,599,776, issued Feb. 4, 1997, both to Burts, Jr., disclose the use of various comminuted plant materials as lost circulation materials.
U.S. Pat. No. 4,957,166, issued Sep. 18, 1990 to Sydansk, discloses the use of a water soluble carboxylate crosslinking polymer along with a chromic carboxylate complex crosslinking agent as a lost circulation material. Sydansk further teaches that the performance requirements of conformance improvement treatment polymers are different from those of lost circulation polymers. Thus, while U.S. Pat. No. 5,377,760, issued Jan. 3, 1995 to Merrill discloses addition of fibers to an aqueous solution of partially hydrolyzed polyacrylamide polymer, with subsequent injection into the subterranean to improve conformance, Sydansk teaches that such would not necessarily work for lost circulation treatment.
Additionally, Merrill's conformance treatment method of mixing the fibers with the polymer solution followed by injection, requires a multiplicity of storage and mixing tanks, and a metering system which must be operated during the operation of the well. Specifically, a first tank will store a water and polymer solution, a second tank will store a water and cross-linking solution, and a third tank will be used to mix fibers with polymer solution from the first tank to create a polymer/fiber slurry. This polymer/fiber slurry is then metered from the third tank and combined with crosslinking solution metered from the second tank to the well bore.
Thus, in spite of the advancements in the prior art, there still need for further innovation in the lost circulation additives.
There is need for further innovation for lost circulation additives utilizing a water soluble polymer.
There is another need for a lost circulation additive which would allow for simplification of the mixing equipment.
These and other needs in the art will become apparent to those of skill in the art upon review of this specification, including its drawings and claims.